In July i went up the Green River Gorge on I-26 in North Carolina it's a 7% Grade. Coming from South Carolina. I was doing 3000 RPM at 40 MPH in the right side truck lane. My truck is a 2002 Dodge Ram...
R will always depend on which gear you are using to tow. Sounds like your truck needed second gear for the pull and nothing wrong with that. Put truck in second gear and drive 40mph anywhere when not towing and you should see the same rpm